The present invention is generally related to medical treatments such as interstitial Brachytherapy. Cancers and other malignant tumors are often treated by surgical resection followed by radiation therapy which targets the residual tumor margin. The radiation therapy can be administered through various methods including external-beam radiation, stereotactic radiosurgery, and permanent or temporary brachytherapy. It is often desirable during diagnosis and treatment to be able to accurately mark a subcutaneous site. For example, the site of a biopsy may be marked to facilitate a surgical procedure or delivery of medicine or radiation treatment. One device for marking a site is a marker wire. The marker wire may be a wire, sheathed wire, or tube which is introduced to the subcutaneous site via a lumen and then secured in place. It is known to use surgical tape to secure the marker wire in place. Alternatively, a feature such as a jog or kink in the marker wire may be positioned such that an interference fit is established between the marker wire and the inner surface of the lumen. However, these methods can be unreliable. For example, it is difficult to make a jog in a tube.